The present invention relates to a golf club shaft capable of increasing the flight distance of a golf ball, and more particularly to a technology for increasing the flight distance of, for example, golfers having a high swing speed by increasing the rigidity of a golf club shaft while lightening the weight of the shaft.
In general, swing form and swing speed greatly vary with every golfer. Therefore, in order to increase the flight distance by optimizing the flexure of a golf club shaft with comfortable swing to thereby accelerate the swing speed of a golf club head (hereinafter referred to as “head speed”), golf club shafts must be those suited to respective golfers. Optimum flexure of a golf club shaft during swing will accelerate the head speed just before striking a golf ball and will increase the dynamic loft angle to provide an optimum angle of striking out a golf ball.
Thus, the weight, flexural rigidity and so on of a golf club shaft are set according to ability, swing form, liking, etc. of a golfer. For example, since most of professional and high class golfers have a great physical strength and a proper swing form, they tend to be able to sufficiently bend the shaft and tend to have a high swing speed. Therefore, to golf clubs for them is generally attached a shaft having a heavy weight and a high flexural rigidity. On the other hand, beginner's class and senior golfers are not able to perform a swing sufficiently utilizing a flexure of a golf club shaft and the swing speed tends to be relatively low. Therefore, in golf clubs for them, it is general to use a golf club shaft having a light weight and a low flexural rigidity. Like this, conventional golf club shafts are roughly classified into such two types of shafts, namely a heavy weight high rigidity shaft and a lightweight low rigidity shaft.
If a golfer who does not have a great physical strength but can swing a golf club at a high speed so as to bend the shaft by twisting of the upper body and body turn during swing, uses a heavy weight high rigidity shaft, the golfer cannot surely swing the club to a finish and, therefore, there arises a problem that the face of a club head does not completely return, so the flight direction of a golf ball is not stabilized. On the other hand, if the golfer uses a lightweight low rigidity shaft, frequently the direction of the face is not stabilized when striking a golf ball due to excess flexure of the shaft during the swing, so the flight direction is not stable.
In order to eliminate disadvantages of lightweight shafts such as poor flight direction performance, decrease in strength and so on, it is proposed, for example, to provide a shaft with a specific distribution of flexural rigidity or to change the flexural rigidity of a specific portion of the shaft such as a tip portion or butt portion of the shaft. On the other hand, in recent years, golf club shafts made of a fiber-reinforced resin are popularly used, since adjustment of the weight, flexural rigidity and so on of the shafts can be relatively easily conducted as compared with metal shafts. For example, JP-A-2002-253714 discloses a lightweight golf club shaft made of a fiber-reinforced resin wherein the flexural rigidity of a grip portion of the shaft is set to a specific range in order to improve the flight distance and the vibration dampening property.
It is an object of the present invention to provide a golf club shaft that even beginner's class and senior golfers can convey a swing power to a golf club head up to the maximum without changing their swing timing and can stabilize the flight direction of a golf ball.
Another object of the present invention is to provide a lightweight golf club which is suitable for golfers having a small muscular strength and a high swing speed and which has a stabilized flight direction performance.
These and other objects of the present invention will become apparent from the description hereinafter.